Security token mismatch

Error message

Security token mismatch. Please refresh the page!

Cause

This error usually means that on your website's server the session folder is not writable or doesn't exists, probably isn't even set. This is about the 'session.save_path' setting in the php.ini of the server. Create a test file (let's call it info.php) with this code:

<?php
$path = ini_get('session.save_path');
echo 'session.save_path: ' . '<br>';
var_dump($path);
echo '<br>is_writable: ';
var_dump(is_writable($path));

then upload it into your FTP and take a look at it in your browser: http://example.com/info.php

You will probably see something similar:

session.save_path: 
string(0) "" 
is_writable: bool(false)

Which means, that the session.save_path is not set. You should contact your server host to help you resolve the problem! 

If you see something different, the result should be that the session.save_path has to be a path, like "/this/is/a/path" and the is_writable has to be "true". If it's not what you see, contact the server host.